1. Field of the Invention
The present invention relates to a fuel cell, and more specifically, to a catalyst layer used for a membrane electrode assembly provided in a fuel cell.
2. Description of the Related Art
Recently, fuel cells which achieve high efficiency in energy conversion and do not produce harmful substances by the power generation reaction, attract attentions. As one type of such fuel cells, the polymer electrolyte fuel cells (PEFC), which operate at a temperature below 100° C., are known.
The PEFC is a power generating apparatus having a basic structure in which a polymer membrane, an electrolyte membrane, is interposed between an anode and a cathode, and a fuel gas including hydrogen is fed to the anode and an oxidant gas including air to the cathode, thereby generating power according to the following electrochemical reactions.
Anode: H2 →2H++2e− (1)
Cathode: ½ O2+2H++2e−→H2O (2)
The anode and the cathode are respectively composed of structures in which a catalyst layer and a gas diffusion layer are laminated. A fuel cell is structured by opposing catalyst layers of each electrode to each other, with a polymer membrane being interposed between the catalyst layers. The catalyst layer is produced by binding carbon particles which carry catalyst with an ion exchange resin. The gas diffusion layer is a passage channel for an oxidant gas and a fuel gas.
In the anode, hydrogen contained in the fed fuel is resolved into hydrogen ions and electrons as represented in Formula (1). Of the two, the hydrogen ion moves toward the cathode within the polymer electrolyte membrane, while the electron towards the cathode through an external channel. On the other hand, in the cathode, oxygen contained in an oxidant gas fed to the cathode reacts with the hydrogen ion moving from the anode to produce water as represented in Formula (2). As the electron moves from the anode to the cathode within the external channel in this way, power can be taken out from the external channel.